Antenna arrangements for implantable therapy device

ABSTRACT

Embodiments of an implantable medical device includes a loop antenna wound about an inner housing. The loop antenna may form a partial winding, a complete winding, or multiple windings about the inner housing. One or more additional antennae may be capacitively coupled to the loop antenna external to the inner housing to increase efficiency and decrease Return Loss Response of the implantable device. The additional antenna may be balanced or unbalanced antennae.

BACKGROUND

Implantable medical devices, including neurological devices and cardiacrhythm management devices, such as pacemakers and implantablecardioverter/defibrillators, typically have the capability tocommunicate data and commands with a device called an externalprogrammer via a radio-frequency telemetry link. A clinician may usesuch an external programmer to program the operating parameters of theimplantable medical device. Furthermore, such characteristics may bemodified after implantation in this manner. Additionally, someimplantable medical devices, most notably neurological devices, containrechargeable batteries, which are recharged via low frequency,near-field telemetry.

Modern implantable devices also include the capability for bidirectionalcommunication so that information can be radiated to the externalprogrammer from the implantable device. Among the data which maytypically be telemetered to and from an implantable device are variousoperating parameters and physiological data, the latter either collectedin real-time or stored from previous monitoring operations. Examples ofcommands telemetered to and from an implantable device may includeinstructions to begin or end treatment or instructions to utilize aparticular treatment schedule or predetermined treatment program.

Telemetry systems for implantable medical devices may utilizeradio-frequency energy to enable bidirectional communication between theimplantable device and an external programmer.

SUMMARY

This invention pertains to implantable medical devices such asimplantable neurostimulators, neuroblockers or neuromodulators. Inparticular, the invention relates to an apparatus and method forenabling radio-frequency telemetry in such devices.

According to aspects of the disclosure, an implantable medical deviceincludes an antenna arrangement including a loop antenna wound about aninner housing.

According to other aspects of the disclosure, an implantable deviceincludes an antenna arrangement including a loop antenna capacitivelycoupled to one or more additional antennae located external to the innerhousing to increase antenna aperture of the additional antennae. Theadditional antennae may be balanced or unbalanced.

The methods, systems, and devices as described herein are applicable toa wide variety of therapies including cardiac pacing with electrodesapplied to heart tissue, gastrointestinal disorders such as obesity,pancreatitis, irritable bowel syndrome, inflammatory disorders, anddiabetes. In an embodiments, methods, systems, and devices are providedfor the treatment of a gastrointestinal disorder by the application of ahigh frequency signal to the vagus nerve of a patient.

Implantable therapy systems are disclosed herein for applying therapy toan internal anatomical feature of a patient.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic block diagram of an example therapy system fortreating a medical condition, such as obesity, in accordance with theprinciples of the present disclosure as described herein;

FIG. 2 is a schematic block diagram of another example therapy systemincluding an implantable device, an external component, and a therapyelement in accordance with the principles of the present disclosure asdescribed herein;

FIG. 3 is a schematic block diagram of one example antennae arrangementincluding an unloaded loop antenna that provides a control against whichthe Return Loss Response of other antennae configurations may becompared in accordance with the principles of the present disclosure asdescribed herein;

FIG. 4 is a first graph plotting the Return Loss Response of theunloaded loop antenna of the first antenna arrangement of FIG. 3 as afunction of frequency in accordance with the principles of the presentdisclosure as described herein;

FIG. 5 is a schematic block diagram of another example antennaearrangement including a loaded loop antenna in accordance with theprinciples of the present disclosure as described herein;

FIG. 6 is a second graph plotting the Return Loss Response of the loadedloop antenna of the second antenna arrangement of FIG. 5 as a functionof frequency in accordance with the principles of the present disclosureas described herein;

FIG. 7 is a schematic block diagram of a third antennae arrangementincluding an unbalanced antenna in accordance with the principles of thepresent disclosure as described herein;

FIG. 8 is a third graph plotting the Return Loss Response of theunbalanced antenna of the third antenna arrangement of FIG. 7 as afunction of frequency in accordance with the principles of the presentdisclosure as described herein;

FIG. 9 is a schematic block diagram of a fourth example antennaarrangement including an unbalanced antenna capacitively coupled to aloaded loop antenna in accordance with the principles of the presentdisclosure as described herein;

FIG. 10 is a fourth graph plotting the Return Loss Response of theunbalanced antenna of the fourth antenna arrangement of FIG. 9 as afunction of frequency in accordance with the principles of the presentdisclosure as described herein;

FIG. 11 is a schematic block diagram of a fifth example antennaarrangement including an unbalanced antenna decoupled from a loaded loopantenna in accordance with the principles of the present disclosure asdescribed herein;

FIG. 12 is a fifth graph plotting the Return Loss Response of theunbalanced antenna of the fifth antenna arrangement of FIG. 11 as afunction of frequency in accordance with the principles of the presentdisclosure as described herein;

FIG. 13 is a schematic block diagram of an implantable device includinga loop antenna wound around a housing and entering the housing at afirst port in accordance with the principles of the present disclosureas described herein;

FIG. 14 is a schematic block diagram of an implantable device includingand a loop antenna having a sharp edge embedded within a dielectricmaterial in accordance with the principles of the present disclosure asdescribed herein;

FIG. 15 is a schematic block diagram of an implantable device includingand a loop antenna and an unbalanced antenna having a sharp edgeembedded within a dielectric material in accordance with the principlesof the present disclosure as described herein;

FIG. 16 is a schematic block diagram of an implantable device includinga loop antenna fully embedded within a dielectric material and woundaround a housing in accordance with the principles of the presentdisclosure as described herein;

FIG. 17 is a schematic block diagram of an implantable device includinga loop antenna wound around a housing with both the loop antenna and thehousing being fully embedded within a dielectric material in accordancewith the principles of the present disclosure as described herein;

FIG. 18 is a schematic block diagram of an implantable device includinga loop antenna wound around a housing with the loop antenna being fullyembedded within a dielectric material and the housing being partiallyembedded within the dielectric material in accordance with theprinciples of the present disclosure as described herein;

FIG. 19 is a schematic block diagram of a simple loop antenna arrangedin free space (i.e., completely outside the three-layer structure ofFIG. 20) in accordance with the principles of the present disclosure asdescribed herein;

FIG. 20 is a schematic block diagram of a simple loop antenna arrangedwithin an outer layer (and outside an insulating layer) of a three-layerstructure in accordance with the principles of the present disclosure asdescribed herein;

FIG. 21 is a schematic block diagram of a simple loop antenna having afirst part arranged within an outer layer of the three-layer structureof FIG. 20 and a second part arranged within an insulating layer inaccordance with the principles of the present disclosure as describedherein;

FIG. 22 is a schematic block diagram of a simple loop antenna arrangedcompletely within an insulating layer of the three-layer structure ofFIG. 20 in accordance with the principles of the present disclosure asdescribed herein;

FIG. 23 is a graph plotting the lowest dip of a Return Loss Response ofeach of the loop antenna arrangements shown in FIGS. 19-22 as a functionof frequency in accordance with the principles of the present disclosureas described herein;

FIG. 24 is a schematic block diagram of an implantable device having anantenna arrangement including an array of antennae capacitively coupledto a loop antenna, the antenna arrangement being coupled to an innerhousing in accordance with the principles of the present disclosure asdescribed herein;

FIG. 25 is a perspective view of an implantable device having a loopantenna wrapped around an inner housing and capacitively coupled to asecond antenna protruding from the inner housing in accordance with theprinciples of the present disclosure as described herein;

FIG. 26 is a front view of the implantable device of FIG. 25 inaccordance with the principles of the present disclosure as describedherein;

FIG. 27 is a side view of the implantable device of FIG. 25 inaccordance with the principles of the present disclosure as describedherein;

FIG. 28 is a perspective view of another implantable device having aloop antenna wrapped around an inner housing and moderately coupled to asecond antenna protruding from the inner housing in accordance with theprinciples of the present disclosure as described herein;

FIG. 29 is a front view of the implantable device of FIG. 28 inaccordance with the principles of the present disclosure as describedherein;

FIG. 30 is a side view of the implantable device of FIG. 28 inaccordance with the principles of the present disclosure as describedherein;

FIG. 31 is a perspective view of an implantable device having a loopantenna wrapped around an inner housing and decoupled from a secondantenna protruding from the inner housing in accordance with theprinciples of the present disclosure as described herein;

FIG. 32 is a front view of the implantable device of FIG. 31 inaccordance with the principles of the present disclosure as describedherein;

FIG. 33 is a side view of the implantable device of FIG. 31 inaccordance with the principles of the present disclosure as describedherein; and

FIG. 34 is a schematic block diagram of an example implantable deviceincluding a loop antenna wound around a housing and configured inaccordance with the principles of the present disclosure as describedherein.

DETAILED DESCRIPTION

The methods, devices and systems as described herein are applicable totreating a wide variety of medical conditions, such as cardiacarrhythmias or other cardio-pulmonary conditions, pancreatitis,diabetes, incontinence, gastro-esophageal reflux disease (GERD), orobesity or other gastro-intestinal disorders. The methods, devices andsystems as described herein also may be applicable to pain management,tissue ablation systems, implantable drug pumps (e.g., insulin pumps),and implantable condition monitoring devices.

In embodiments, the disclosure provides an implantable medical devicecomprising: an inner housing containing a processor and a communicationscircuit; a first antenna arrangement wrapped circumferentially aroundthe inner housing, the first antenna arrangement having a first port atwhich the first antenna arrangement enters the inner housing, the firstantenna arrangement being electrically coupled to the communicationscircuit via the first port, the first antenna arrangement including aloop antenna that is electrically coupled to the communications circuitvia the first port; and a second antenna arrangement arranged externalof the inner housing, the second antenna arrangement having a secondport at which the second antenna arrangement enters the inner housing,the second antenna arrangement being capacitively coupled to the loopantenna; wherein the implantable medical device is configured forimplantation within a body of a patient.

Another aspect of the disclosure provides a method for communicatingwith an implantable device, the method comprising: providing animplantable device including a loop antenna wound around an exterior ofan inner housing containing a processor, a communications circuit, arechargeable power source, and a switching circuit, the implantabledevice also including a second antenna capacitively coupled to the loopantenna; implanting the implantable device within the patient;transmitting a power signal to the implantable device to provide powerto the rechargeable power source, the power signal having a firstfrequency; and transmitting a communication signal to the implantabledevice to provide data or commands to the communications circuit. In oneembodiment, the communications signal has a second frequency that ishigher than the first frequency.

DEFINITIONS

As the term is used herein, an antenna arrangement includes anarrangement of one or more antennae. If the antenna arrangement includesmultiple antennae, then each antenna in the arrangement may becapacitively coupled or decoupled from each of the other antennae.

ILLUSTRATED EMBODIMENTS

With reference now to the various drawing figures in which identicalelements are numbered identically throughout, a description of thepreferred embodiments of the present invention will now be described.

FIG. 1 is a schematic block diagram of a therapy system 100 for treatinga medical condition, such as obesity. The therapy system 100 includes asealed implantable device 105, at least one therapy and/or diagnosticelement 170, and an external component 160 configured to communicatewith the implantable device 105 via an implantable antenna arrangement120. The implantable device 105 and implantable antenna arrangement 120are adapted for implantation beneath the skin layer 130 of a patient tobe treated. In some embodiments, the implanatable device is hermeticallysealed.

In general, the implantable device 105 includes a housing 106 thatprovides a sealed enclosure in which circuitry of the implantable devicemay be housed. In the example shown in FIGS. 1 and 2, the housing 106contains a communications circuit (e.g., an RF module) 110 and atreatment module 115. In one embodiment, the housing 106 provideselectrical shielding for the RF module 110 and the treatment module 115.In another embodiment, the housing 106 may provide a grounding plane forone or more antennae of the antenna arrangement 120 coupled to theimplantable device 105. For example, the housing 106 may be formed fromone or more conductive materials (e.g., Titanium, Niobium, Platinum,Indium, stainless steel, MP35N alloys, or other biocompatiblematerials). In another embodiment, the housing 106 may be plated with aconductive material (e.g., Gold plated over Copper). In otherembodiments, however, non-conductive layers may be added in or aroundall or part of the housing 106 as will be disclosed in greater detailherein.

In general, the treatment module 115 manages treatment of the patient.The treatment module 115 is configured to communicate with the therapyelement and/or diagnostic element 170. In one embodiment, the treatmentmodule 115 is configured to generate a therapy signal and to communicate(e.g., electrically) the therapy signal to the therapy element (e.g.,lead electrodes) 170 to provide treatment to the patient. In anotherembodiment, the treatment module 115 obtains readings indicating acondition of the patient from a diagnostic device (e.g., a temperaturesensor, an accelerometer, etc.).

The therapy element 170 provides electrical signals (e.g., pulses) to atleast one area of the patient's body in accordance with the therapysignals generated by the treatment module 115. For example, the therapyelement 170 may include two or more electrical lead assemblies (notshown) that couple to nerves, muscles, organs, or other tissue of thepatient. In some embodiments, the electrical lead assembly comprises alead and one or more electrodes. In one embodiment, the therapy and/ordiagnostic element 170 is arranged external to the hermetically sealedimplantable device 105. In another embodiment, the therapy and/ordiagnostic element 170 is arranged within the hermetically sealedimplantable device 105.

In one embodiment, the therapy element 170 up-regulates and/ordown-regulates one or more nerves of a patient based on the therapysignals provided by the treatment module 115. For example, electrodesmay be individually placed on the anterior vagus nerve and posteriorvagus nerve, respectively, of a patient. In embodiments, the placementof the electrodes on the vagus nerve may vary. In an embodiment theelectrode is placed below the innervation of the heart such as in subdiaphragmatic location. In other embodiments, however, fewer or greaterelectrodes can be placed on or near fewer or greater nerves. In stillother embodiments, the therapy element 170 may provide electricalsignals directly to the patient's organs, such as the heart, lungs,and/or stomach, or to the patient's muscles, such as the sphinctermuscle, or to other tissue of the patient.

The external component 160 includes circuitry for communicating with theimplantable device 105. In general, communication is transmitted throughthe skin 130 of the patient along a two-way signal path as indicated bydouble-headed arrow 150. Example communication signals include powersignals, data signals, and command signals. In general, the RF module110 controls when power signals, data signals, and/or command signalsare radiated to and from the implantable device 105 within thenear-field and/or the far-field.

In the example shown, the external component 160 can communicate withthe implantable device 105 via bidirectional telemetry (e.g. viaradiofrequency (RF) signals). In one embodiment, the external component160 may provide power to the implantable device 105 via an RF link. Inanother embodiment, treatment instructions include treatment parameters,signal parameters, implantable device settings, treatment schedule,patient data, command signals, or other such signals may be communicatedbetween the external component 160 and the implantable device 105.

The external component 160 shown in FIG. 1 includes another antennaarrangement 165 that can send and receive RF signals. The implantableantenna arrangement 120 may be implanted within the patient and coupledto the RF module 110 of the implantable device 105. In one embodiment,the implantable antenna arrangement 120 is integral with the implantabledevice 105. The implantable antenna arrangement 120 serves to radiate(e.g., receive and transmit) signals from and to the antenna arrangement165 of the external component 160 within the near-field and/or thefar-field. In one embodiment, the RF module 110 includes a matchingcircuit that optimizes the impedance of the antenna arrangement 120 fora particular frequency.

In some embodiments, the external component 160 and the RF module 110can encode and decode information signals as bit streams by amplitudemodulating, frequency modulating, or rectifying an RF carrier wave. Inone embodiment, the signals radiated between the antenna arrangements165, 120 have a carrier frequency of about 6.78 MHz. In otherembodiments, however, higher or lower carrier wave frequencies and/orrectification levels may be used and other modulation methods and levelsmay be used.

In one embodiment, the implantable device 105 communicates with theexternal component 160 using load shifting. For example, load shiffingcan be achieved by modification of the load induced on the externalcomponent 160. This change in the load can be sensed by the inductivelycoupled external component 160. In other embodiments, however, theimplantable device 105 and external component 160 can communicate usingother types of signals.

In some embodiments, the RF module 110 of the implantable device 105receives power from the external component 160. In some embodiments, theRF module 110 distributes the power to the treatment module 115 togenerate the therapy signals. In one such embodiment, the treatmentmodule 115 may depend entirely upon power received from an externalsource (e.g., the external component 160 or another external powersource). In another embodiment, an implantable power source 117, such asa rechargeable battery, supplies the power to generate the therapysignals. In such an embodiment, the RF module 110 may distribute thepower received from the external component 160 to the implantable powersource 117 for recharging.

In some embodiments, the treatment module 115 initiates the generationand transmission of therapy signals to the therapy elements 170. In anembodiment, the treatment module 115 initiates therapy when powered bythe implantable power source 117. In other embodiments, however, theexternal component 160 triggers the treatment module 115 to begingenerating therapy signals. After receiving initiation signals from theexternal component 160, the treatment module 115 generates the therapysignals and transmits the therapy signals to the therapy elements 170.

In other embodiments, the external component 160 also can provide theinstructions according to which the therapy signals are generated.Example parameters of therapy signals may include pulse-width,amplitude, frequency, ramping, duty cycle, treatment schedule, and othersuch parameters. In a preferred embodiment, the external component 160includes memory in which several predetermined programs/therapyschedules can be stored for transmission to the implantable device 105.The external component 160 also can enable a user to select aprogram/therapy schedule stored in memory for transmission to theimplantable device 105. In another embodiment, the external component160 can provide treatment instructions with each initiation signal.

Typically, each of the programs/therapy schedules stored on the externalcomponent 160 can be adjusted by a physician to suit the individualneeds of the patient. For example, a computing device (e.g., a notebookcomputer, a personal computer, etc.) (not shown) can be communicativelyconnected to the external component 160. With such a connectionestablished, a physician can use the computing device to programtherapies into the external component 160 for either storage ortransmission to the implantable device 105.

The implantable device 105 also may include memory (not shown) in whichtreatment instructions and/or patient data can be stored. For example,the implantable device 105 can store therapy programs indicating whattherapy should be delivered to the patient. The implantable device 105also can store patient data indicating how the patient utilized thetherapy system 100 and/or reacted to the delivered therapy.

In a specific embodiment, as described below, the implantable device 105contains a rechargeable battery from which the implantable device 105may draw power.

FIG. 2 is a schematic block diagram of another therapy system 100′including an implantable device 105′, an external component 160, and atherapy element 170. The implantable device 105′ includes at least oneRF module 110, a treatment module 115, and an antenna arrangement 120′including a first antenna arrangement 122 and a second antennaarrangement 124. In general, the first antenna arrangement 122 includesa loop antenna.

In one embodiment, the second antenna arrangement 124 includes anunbalanced antenna including, for example, an inverted-L antenna, azigzag antenna, a helical antenna, a spiral antenna, a folded antenna, aserpentine antenna, or any other suitable antenna that is capacitivelycoupled to the first antenna arrangement 122. In another embodiment, thesecond antenna arrangement 124 includes a loop antenna that iscapacitively coupled to the first antenna arrangement 122. In otherembodiments, one or more antennae of the second antenna arrangement 124may be decoupled from the antennae of the first antenna arrangement 122.

In some embodiments, the first antenna arrangement 122 receives power(see arrow 152) with which to operate the implantable device 105′ and/orto recharge the power source 117. The second antenna arrangement 124receives and transmits communication signals containing information(e.g., therapy parameters, schedules, patient data, etc.) and/or commandsignals (see arrow 154) from and to the external component 160.Advantageously, separating the functions of the antenna arrangements122, 124 may allow for concurrent radiation of power and communicationsignals (e.g., commands and/or data). Separating the functions also mayenable tuning each antenna arrangement 122, 124 to better implement aparticular function, such as communication range or charging efficiency.In one embodiment, the first antenna arrangement 122 also can receiveand transmit information signals from and to the external component 160.

In other embodiments, the second antenna arrangement 124 may include anarray of antennae (e.g., see FIG. 24). Each of the antennae in theantennae array may be capacitively coupled or decoupled to or from thefirst antenna arrangement 122 and/or each other antenna in the antennaearray. As will be described in greater detail herein, the antennae ofthe array may be utilized to modify the direction, polarization, and/orgain of the information signals received and transmitted by the firstantenna 122. Providing diversified antennae within the implantabledevice 105′ also may enable tailoring of the RF signal to accommodatethe location and/or orientation of the implantable device 105′ withrespect to an external source. Additional antennae also may be utilizedto locate the implantable device 105′ with respect to an externalobject, such as the external component 160.

Antenna Arrangements

The systems and devices as described herein comprise one or more antennaarrangements. The antenna arrangements facilitate communication andpower signals as described herein. In embodiments, an implantable devicecomprises a first antenna arrangement wrapped circumferentially aroundthe inner housing, the first antenna arrangement having a first port atwhich the first antenna arrangement enters the inner housing, the firstantenna arrangement being electrically coupled to the communicationscircuit via the first port, the first antenna arrangement including aloop antenna that is electrically coupled to the communications circuitvia the first port. The implantable device also may comprise a secondantenna arrangement arranged external of the inner housing, the secondantenna arrangement having a second port at which the second antennaarrangement enters the inner housing, the second antenna arrangementbeing capacitively coupled to the loop antenna. In some embodiments, thefirst and second antenna arrangements transmit at different frequencies.

Referring to FIGS. 3-12, different antenna arrangements andconfigurations may be utilized in the implantable devices disclosedherein, e.g., as implantable antenna arrangement 120. In FIGS. 3-12, theradiation capabilities of different types of antenna arrangements areshown relative to one another. In particular, five different types ofantenna arrangements are presented and a numerically simulated ReturnLoss Response for each in free space is shown. The antenna arrangementsin FIGS. 3-12 are not coupled to implantable devices. Rather, thenumerical simulations are provided for the antenna arrangementspositioned in free space in order to compare the radiation capabilitiesof the different antenna arrangements.

Return Loss Response (dB) is defined as a ratio of reflected signalpower over input signal power. The Simulated Return Loss Response foreach antenna arrangement provides information about the resonantfrequencies, transmission range, radiation efficiency, and the number ofresonant frequencies of the antenna arrangement. For example, dips inthe Simulated Return Loss Response generally correspond with resonantfrequencies of the antenna arrangement. Furthermore, the amplitude ofthe dips in the Simulated Return Loss Response generally correspondswith the efficiency (and hence power) of the antenna arrangement.

The Simulated Return Loss Response provides for a selection of differentantenna arrangements depending on the requirements for a particulartherapy system. For example, in some embodiments, it is desirable totransmit a power signal and a communication signal concurrently. Inother embodiments, it may be desirable to eliminate a matching circuitin the device. In other embodiments, it may be desirable to eliminateresonant frequencies from an antenna arrangement.

For example, FIG. 3 is a schematic block diagram of a first exampleantenna arrangement 200 that may be used in the implantable devicesdisclosed herein. The antenna arrangement 200 includes a loop antenna210 having a first port 211. In one embodiment, the loop antenna 210 ofantenna arrangement 200 may be utilized with an implantable device as animplantable antenna (e.g., antenna 120 of FIGS. 1 and 2).Advantageously, the loop antenna 210 may enable magnetic coupling of animplantable device (e.g., implantable device 105 of FIG. 1) to anexternal component (e.g., external component 160 of FIG. 1) for powerand/or communication (e.g., command signals and/or data signals)transference.

FIG. 4 is a first graph 300 plotting a Simulated Return Loss Response330 of the first port 211 of the first antenna arrangement 200 as afunction of frequency. The results plotted in the first graph 300 wereobtained using a mathematical model (i.e., numerical simulation) of aloop antenna in free space separate from an implantable device.Accordingly, the first graph 300 (i.e., as well as the graphs shown inFIGS. 6, 8, 10, and 12) are provided to disclose the relative RFradiation capability of each antenna arrangement with respect to eachother and not to describe the actual radiation capability of theimplantable system.

The first graph 300 includes a first axis 310 representing the ReturnLoss Response (dB) of the loop antenna 210 as measured at the first port211. The first axis 310 ranges from about −7 decibels (dB) to about 1dB. The first graph 300 also includes a second axis 320 representing thefrequency of the loop antenna 210. The second axis 320 ranges from about0 gigahertz (GHz) to about 3 GHz. As shown in the first graph 300, theReturn Loss Response 330 has a first dip 332 of about −6.5 dB at afrequency of approximately 0.45 GHz. Additional dips (e.g., see 334)occur at higher signal frequencies. This configuration may be desirableif a low resonant frequency and/or a lower amplitude, high resonantfrequency is desired. As the amplitude of the dips in FIG. 4 tends to belower than in other configurations described herein, the radiationcapability of this configuration is lesser than some of the otherconfigurations.

FIG. 5 is a schematic block diagram of a second example antennaarrangement 400 including a loaded loop antenna that may be used in theimplantable devices disclosed herein. The second antenna arrangement 400includes the loop antenna 210 of FIG. 1 and a floating conductive plate220 providing a loading effect on the loop antenna 210. For example, theeffects of the conductive plate 220 can represent the loading effects ofa conductive housing on an antenna arrangement in an implantable device.The loop antenna 210 has the first port 211 and is wound one or moretimes around the plate 220 without contacting the plate 220.

In general, the plate 220 affects the Return Loss Response of the loopantenna 210 (e.g., through “the loading effect”) as shown in FIG. 6. Theeffects of the housing 106 of the implantable device 105 on theimplantable antenna 120 (see FIG. 1) mimic these effects of the floatingconductive plate 220 on the loop antenna 210.

FIG. 6 is a second graph 500 plotting the Return Loss Response 530 ofthe first port 211 of the second antenna arrangement 400 as a functionof frequency. The second graph 500 is provided to aid in comparing theradiation capability of the loaded-loop antenna arrangement 400 to otherantenna arrangement (e.g., the unloaded loop antenna arrangement 200 ofFIG. 3) disclosed herein. The results plotted in the second graph 500were obtained using a mathematical model (i.e., numerical simulation) ofa loaded loop antenna in free space separate from an implantable device.

The second graph 500 includes a first axis 510 representing the ReturnLoss Response at the first port 211 of the loaded loop antennaarrangement 400. The first axis 510 ranges from about −20 dB to about 2dB. The second graph 500 also includes a second axis 520 representingthe frequency of the loaded loop antenna arrangement 400. The secondaxis 520 ranges from about 0 GHz to about 3 GHz. As shown in the secondgraph 500, the Return Loss Response 530 has a dip 532 of about −19 dB ata frequency of approximately 0.5 GHz. Additional dips (e.g., see 534)occur at higher signal frequencies.

Accordingly, loading the loop antenna 210 of the first antennaarrangement 200 with a conductive plate 220, as shown in FIG. 5,increases the radiation capability of the antenna arrangement. Theamplitude of the dips (e.g., dips 532, 534) in the Return Loss Response530 has increased. However, the dips in the Simulated Return LossResponse 530 did not shift significantly on the second axis 520.Accordingly, the frequency (i.e., or frequencies) at which the antennaarrangement resonates is not significantly affected.

FIG. 7 is a schematic block diagram of a third antenna arrangement 600including an unbalanced antenna 230 capacitively coupled to a conductiveplate, such as conductive plate 220 of FIG. 5, that may be used in theimplantable devices disclosed herein. The unbalanced antenna 230 has aport 231. In the example shown, the unbalanced antenna 230 includes aninverted-L antenna arranged adjacent to the conductive plate 220. Inother embodiments, however, the unbalanced antenna 230 may include anyunbalanced antenna. Non-limiting examples of a suitable unbalancedantenna 230 include a helical antenna, a spiral antenna, a zigzagantenna, a folded antenna, and a serpentine antenna.

FIG. 8 is a third graph 700 plotting the Return Loss Response 730 at theport 231 of the third antenna arrangement 600 as a function offrequency. The third graph 700 is provided to aid in comparing theradiation capability of the antenna arrangement 600 to other antennaarrangements (e.g., the loaded loop antenna arrangement 400 of FIG. 5)disclosed herein. The results plotted in the third graph 700 wereobtained using a mathematical model (i.e., numerical simulation) of aninverted-L antenna arranged in free space separate from an implantabledevice.

The third graph 700 includes a first axis 710 representing the ReturnLoss Response at the port 231 of the third antenna arrangement 600. Thefirst axis 710 ranges from about −22.5 dB to about 0 dB. The third graph700 also includes a second axis 720 representing the frequency of thethird antenna arrangement 600. The second axis 720 ranges from about 0GHz to about 3 GHz. As shown in the third graph 700, the Return LossResponse 730 at the port 231 has a dip 732 of about −22 dB at afrequency of approximately 1.4 GHz.

As shown in FIG. 8, the third antenna arrangement 600 including theunbalanced antenna 230 radiates more effectively at a higher operatingfrequency (i.e., has a higher resonant frequency) than the loop antennaarrangements 200, 400 disclosed above. Accordingly, the third antennaarrangement 600 is capable of transmitting over a greater distance.

Referring to FIGS. 9-12, providing an antenna arrangement including twoor more antennae may enhance the efficiency of the implantable device.FIG. 9 is a schematic block diagram of an example antenna arrangement800 that may be used in the implantable devices disclosed herein. Ingeneral, the antenna arrangement 800 capacitively couples the loadedloop antenna 400 of FIG. 5 with the unbalanced antenna 600 of FIG. 7.Accordingly, the fourth antenna arrangement 800 includes the loopantenna 210, the conductive plate 220, and the unbalanced antenna 230disclosed herein. In the example shown in FIG. 9, the unbalanced antenna230 is an inverted-L antenna. In other embodiments, however, theunbalanced antenna 230 may includes any suitable unbalanced antennaarranged to capacitively couple to the plate 220 and to the loop antenna210.

Each of the antennae 210, 230 has its own port 211, 231, respectively,at which the Return Loss Response of the antenna 400, 600 may besimulated. FIG. 10 is a fourth graph 900 plotting the Simulated ReturnLoss Response 930 at the first port 211 of the loop antenna 210 of thefourth antenna arrangement 800 as a function of frequency. Accordingly,the Simulated Return Loss Response 930 indicates how capacitivelycoupling the unbalanced antenna to the loop antenna affects theradiation capability of the loop antenna 210.

The fourth graph 900 is provided to aid in comparing the radiationcapability of the fourth antenna arrangement 800 to other antennaarrangement (e.g., the loaded loop antenna arrangement 400 of FIG. 5and/or the unbalanced antenna arrangement 600 of FIG. 7) disclosedherein. The results plotted in the fourth graph 900 were obtained usinga mathematical model (i.e., numerical simulation) of an inverted-Lantenna capacitively coupled to a loaded loop antenna in free spaceseparate from a communications circuit or other part of an implantabledevice.

The fourth graph 900 includes a first axis 910 representing the ReturnLoss Response at port 231 of the unbalanced antenna 230 of the fourthantenna arrangement 800. The first axis 910 ranges from about −22.5 dBto about 0 dB. The fourth graph 900 also includes a second axis 920representing the frequency of the fourth antenna arrangement 800. Thesecond axis 920 ranges from about 0 GHz to about 3 GHz. As shown in thefourth graph 900, the Return Loss Response 930 has a first dip 932 ofabout −16 dB at a frequency of approximately 0.4 GHz, a second dip 934of about −19 dB at about 0.75 GHz, a third dip 936 of about −20 dB atabout 1.2 GHz, and a fourth dip 938 of about −19.5 dB at about 1.5 GHz.Additional dips occur at higher signal frequencies (e.g., see dip 939).

A comparison of the second, third, and fourth graphs 500, 700, 900,respectively, indicates that capacitively coupling an unbalanced antenna(e.g., unbalanced antenna 230 of FIG. 7) to a loaded loop antenna (e.g.,loaded loop antenna 210 of FIG. 5) yields an antenna arrangement with agreater aperture than either antenna individually. Advantageously, theresulting antenna arrangement has an increased radiation efficiency andincreased resonance. In addition, the larger dips in the SimulatedReturn Loss Response at resonant frequencies in FIG. 10 also indicatethe antenna arrangement may utilize less power to transmit over a givenrange or may transmit farther for a given power level.

Furthermore, increasing the aperture of the antenna may enablecommunication at MICS (Medical Implant Communications Service) frequencylevels (e.g., about 0.4 GHz) and WMT (Wireless Medical Telemetry)frequencies levels (about 1.4 GHz) without a matching circuit.Eliminating the matching circuit from the implantable device wouldenable the implantable device to be smaller and manufactured at lowercost. Eliminating the matching circuit also may enhance the reliabilityof the implantable device by reducing the number of parts.

In addition, capacitively coupling an unbalanced antenna (e.g.,unbalanced antenna 230 of FIG. 7) to a loaded loop antenna (e.g., loadedloop antenna 210 of FIG. 5) yields an antenna arrangement having anincreased number of resonant frequencies. For example, the capactivelycoupled antenna arrangement 800 of FIG. 9 has a resonant frequency dip932 at approximately 0.4 GHz and another resonant frequency dip 938 atabout 1.5 GHz (see FIG. 10). In other embodiments, the antennaarrangement 800 could be configured to have a resonant frequency ofabout 6.7 MHz.

Increasing the number of resonant frequencies may increase the number ofsignals that may be obtained by the antenna arrangement. For example,the antenna arrangement, in one embodiment, a capacitively coupledantenna arrangement may be able to radiate power and communicationsignals. In one embodiment, increasing the number of resonantfrequencies may increase the number of signals that may be obtainedconcurrently.

Furthermore, providing an antenna arrangement including multipleantennae enables each antenna to be configured to perform separatefunctions. For example, the antenna arrangement may include a firstantenna (e.g., loop antenna 210) configured to radiate power and asecond antenna (e.g., unbalanced antenna 230) configured to radiatecommunication signals. The first antenna may receive power (e.g., fromabout zero to about three watts) from one or more external components(e.g., see external component 160 of FIG. 2) and the second antenna mayreceive and transmit data (e.g., therapy parameters, treatmentschedules, patient use data, treatment results, etc.) and/or commands(e.g., begin treatment, utilize a given treatment schedule, etc.) fromand to the external components. In one embodiment, the received power isused to recharge an internal power source, such as rechargeable battery117 of FIGS. 1 and 2. In other embodiments, however, a fewer or greaternumber of antennae may be utilized to receive and transmit communicationsignals and/or power signals.

Advantageously, by radiating power over a first antenna andcommunication signals over a second antenna, the power and communicationsignals may be radiated concurrently, thereby enhancing the efficiencyof the implantable device. Furthermore, by separating which functionsare performed by which antennae, each antenna may be tuned to optimizeperformance of its assigned task. For example, the first antenna may bea loop antenna configured to radiate high amplitude RF signals at lowerfrequencies (e.g., over shorter distances) and the second antenna may bean unbalanced antenna configured to radiate RF signals at higherfrequencies (e.g., over longer distances). In such an embodiment, powermay be transferred within the near-field of the antenna arrangement andcommunication signals may be communicated within the far-field of theantenna arrangement.

Decoupling antennae of an antenna arrangement also may provideadvantages. FIG. 11 is a schematic block diagram of a fifth exampleantenna arrangement 1000 that may be used in the implantable devicesdisclosed herein. The fifth antenna arrangement 1000 includes a loopantenna 210 loaded with a conductive plate 220 and another unbalancedantenna 235. Both antennae 210, 235 have ports 211, 236, respectively,at which Return Loss Response may be measured. The unbalanced antenna235 of the fifth antenna arrangement 1000, however, is decoupled fromthe loop antenna 210 (e.g., arranged perpendicular to the loop antenna210). In the example shown in FIG. 11, the unbalanced antenna 235 is avertical monopole antenna. In other embodiments, however, the unbalancedantenna 235 may include any suitable antenna arranged to not couple tothe loop antenna 210.

FIG. 12 is a fifth graph 1100 plotting the Return Loss Response 1130 atthe port 236 of the decoupled monopole antenna 235 of the fifth antennaarrangement 1000 as a function of frequency. The fifth graph 1100 isprovided to aid in comparing the radiation capability of the decoupledantenna arrangement 1000 to other antenna arrangement (e.g., the antennaarrangement 800 of FIG. 9) disclosed herein. The results plotted in thefifth graph 1100 were obtained using a mathematical model (i.e.,numerical simulation) of a monopole antenna decoupled from a loaded loopantenna in free space separate from an implantable device.

The fifth graph 1100 includes a first axis 1110 representing the ReturnLoss Response at the port 236 of the unbalanced antenna 235 of the fifthantenna arrangement 1000. The first axis 1110 ranges from about −25 dBto about 0 dB. The fifth graph 1100 also includes a second axis 1120representing the frequency of the fifth antenna arrangement 1000. Thesecond axis 1120 ranges from about 0 GHz to about 3 GHz. As shown in thefifth graph 1100, the Return Loss Response 1130 of the decoupled antennaarrangement 1000 has a first dip 1132 of about −24 dB at a frequency ofapproximately 1.7 GHz, a second dip 1134 of about −18 dB at about 2.1GHz, and a third dip 1136 of about −13 dB at about 2.5 GHz.

Accordingly, decoupling an unbalanced antenna (e.g., antenna 235) from aloaded loop antenna (e.g., loaded loop antenna 210) shifts the resonantfrequencies of the antenna arrangement to higher frequencies (e.g.,compare FIGS. 6, 8, and 12). Decoupling the antennae also may decreasethe number of resonant frequencies. Advantageously, decreasing thenumber of resonant frequencies may mitigate interference betweendifferent antennae. For example, decoupling the antennae may enablesimultaneous radiation of power signals and communication signals bydifferent antennae without interference.

Insulating the Antenna Arrangements

Referring now to FIGS. 13-23, the radiation capability of differentantenna configurations (balanced antenna configurations and/orunbalanced antenna configurations) may be modified by partially or fullyembedding one or more of the antennae in an insulating layer ofdielectric material. Non limiting examples of insulating dielectricmaterials include biocompatible materials, such as biocompatibleplastics (e.g., silicone rubber, polysulphone, TECOTHANE® offered byLubrizol Advanced Materials, Inc. of Cleveland, Ohio, etc).

FIGS. 13-18 are schematic block diagrams illustrating differentembodiments of an implantable device 1200A, 1200B, 1200C, 1200D, 1200E,1200F, respectively, having an antenna arrangement including a loopantenna 1210 loaded with a conductive medium 1220. In one embodiment,the conductive medium 1220 includes the hermetically sealed innerhousing of an implantable device that contains the circuitry of theimplantable device. In other embodiments, however, the conductive medium1220 may include any conductive surface. In the examples shown in FIGS.13-18, the loaded loop antenna 1210 enters the inner housing 1220 andcouples to components within the housing 1220 via an antenna port 1211.

In FIG. 13, the antenna arrangement of the implantable device 1200A isfully exposed (i.e., no part of the antenna arrangement is enclosedwithin a dielectric medium). Accordingly, antenna arrangement may bearranged in contact with surrounding tissue when implanted within apatient. Non-limiting examples of surrounding tissue may include muscle,fat, nerve, or skin layers of the patient. In the example shown, theantenna arrangement includes a loaded loop antenna 210. In otherembodiments, however, the antenna arrangement may include one or morebalanced and/or unbalanced antennae.

Advantageously, the dielectric constant of the surrounding tissueincreases the aperture of the exposed antenna. Increasing the apertureof the antenna enables a smaller antenna to be utilized. Furthermore,radiating the loop antenna 1210 at lower frequencies (e.g., about 0.4GHz) mitigates radiation efficiency concerns due to return loss, sincehuman tissue tends to be low loss at these lower frequencies. Moreover,the antenna arrangement may cost less and/or be easier to manufacturewithout a dielectric layer.

In FIGS. 14 and 15, sharp edges of the antenna arrangements of theimplantable devices 1200B, 1200C may be partially embedded within aninsulating dielectric medium. In FIG. 14, the antenna arrangementincludes a loop antenna 1210 having a first sharp edge 1213 that isembedded within a dielectric layer 1240. In FIG. 15, the antennaarrangement includes a loop antenna 1210 having sharp corners 1217 thatare embedded within a first dielectric layer 1242 and an unbalancedantenna 1230 having a sharp edge 1233 that is embedded within a seconddielectric layer 1244. In other embodiments, however, the antennaarrangement may include a greater or fewer number of balanced and/orunbalanced antennae.

Portions of the loaded loop antenna 1210 still may be arranged incontact with surrounding tissue when implanted, thereby increasing theaperture of the antenna arrangements. Advantageously, however,insulating the sharp edges of the antenna arrangements may inhibit burnsor other harm to a patient in which the antenna arrangement is implantedwhen the patient is scanned with a Magnetic Resonance Image (MRI)machine. If the sharp edges are left exposed, current induced by themagnetic field that is generated by the MRI machine may build up atthese edges and burn the surrounding tissue. The low dielectric medium(e.g., dielectric layers 1240, 1242, 1244) may inhibit accumulation of ahigh current density at the antenna edges from the effects of themagnetic field created by the MRI machine.

In FIG. 16, the antenna arrangement of the implantable device 1200D isfully embedded within a layer of dielectric medium 1240. In the exampleshown, the antenna arrangement includes the loaded loop antenna 210. Inother embodiments, however, the antenna arrangement may include one ormore balanced and/or unbalanced antennae. After implantation, theimplantable device 1200D may contact different types of surroundingtissue (e.g., fat, muscle, nerves, etc.). Each type of surroundingtissue may have different dielectric constants.

Embedding the antenna arrangement in the layer of dielectric mediuminsulates the antenna arrangement from effects of the dielectricconstant of the surrounding medium. Accordingly, insulating the antennaarrangement in the dielectric material advantageously may enhancerepeatability of performance by providing surrounding media (e.g., thedielectric layer 1240) having a consistent dielectric constant.Furthermore, when operating at higher frequencies (e.g., about 1.4 GHz),human tissue tends to be lossy (i.e., higher frequency signals tend todegrade as they travels through human tissue). Accordingly, insulatingthe antenna arrangement from the surrounding tissue may enhance theradiation efficiency of the antenna arrangement at higher frequencies.Moreover, if the dielectric layer is formed from a biocompatiblematerial, then embedding the antenna arrangement within the dielectriclayer may enhance the biocompatibility of the antenna arrangement.

In FIG. 17, the dielectric layer 1240 extends over the inner housing1220 as well as the antenna arrangement (e.g., loaded loop antenna 1210)of the fifth implantable device 1200E. Advantageously, embedding theinner housing 1220 within the dielectric layer 1240 may increase theaperture of the antenna arrangement. For example, embedding the innerhousing 1220 that loads the loop antenna 1210 may increase the apertureof the loop antenna 1210 by inhibiting the surface current on theperiphery of the inner housing 1220. Furthermore, embedding the innerhousing 1220 within the dielectric layer 1240 also may improve thebiocompatibility of the implantable device 1220.

In FIG. 18, a first dielectric layer 1240 extends over the antennaarrangement of the sixth implantable device 1200F and a seconddielectric layer 1245 partially embeds the inner housing 1220. In oneembodiment, the antenna arrangement includes a loaded loop antenna 1210.In other embodiments, however, the antenna arrangement may include oneor more balanced and/or unbalanced antennae. Partially embedding theinner housing 1220 within a dielectric layer may increase the apertureof the antenna arrangement. In one embodiment, the section of the innerhousing 1220 adjacent the port of the antenna arrangement (e.g., port1211 of the loaded loop antenna 1210) may be embedded within adielectric medium to increase the aperture of the antenna arrangement.Advantageously, exposed portions of the inner housing 1220 may be usedto provide treatment to the patient (e.g., as an electrode).

Implantation environments for the antenna arrangement tend to vary bypatient and even within the same patient. For example, the dielectricconstant of tissue surrounding an antenna arrangement implanted withinthe patient may vary over the surface area of the antenna arrangement(e.g., when a first portion of the antenna arrangement contacts a nerveand a second portion of the antenna arrangement contacts muscle).Accordingly, to enhance understanding of the effects of the dielectricmedium, the simulation is directed to a simple loop antenna 1310arranged within a simplified implantation environment represented by athree-layer structure 1300 (see FIGS. 19-22).

In FIGS. 19-22, the three-layer structure 1300 includes an inner layer1340 having a first dielectric constant ∈1 arranged between two outerlayers 1360, each of which have a second dielectric constant ∈2. Ingeneral, the insulating layer 1340 represents a layer of dielectricmedium (e.g., the dielectric layer 1240 shown in FIGS. 14-18) and theouter layers 1360 represent human tissue surrounding the implantabledevice. Accordingly, the first dielectric constant ∈1 of the inner layer1340 is less than the second dielectric constant ∈2 of the outer layers1360.

For ease in computation and understanding in the simulation, a thicknessH of about 10 mm and a dielectric constant ∈1 of about 1 were selectedfor the inner layer 1340 and a thickness T of about 150 mm and adielectric constant ∈2 of about 10 were selected for each of the outerlayers 1360. These measurements do not necessarily represent preferreddimensions and properties of the antenna arrangement or of theimplantation environment. Rather, these measurements provide a simplemodel from which a numerical simulation may be computed to facilitateexplanation and testing of the concept. In other embodiments, the outerlayers 1360 may have different dielectric constants and/or thicknessesfrom one another.

FIG. 19 is a schematic block diagram of the loop antenna 1310 arrangedwithin free space (i.e., completely outside the three-layer structure1300). Accordingly, the loop antenna 1310 represents an implantabledevice having an antenna fully exposed to free space (e.g., air). Forexample, the loop antenna 1310 of FIG. 19 may represent an antennaarrangement of an implantable device before implantation.

FIG. 20 is a schematic block diagram of the loop antenna 1310 arrangedwithin one of the outer layers 1360 of the three-layer structure 1300and outside the inner layer 1340. The loop antenna 1310 represents animplantable device having an antenna arrangement fully exposed to thesurrounding tissue of the patient. For example, the loop antenna 1310 ofFIG. 20 may represent the loaded loop antenna 1210 of FIG. 13, which isnot insulated within an outer layer of a dielectric medium, afterimplantation.

FIG. 21 is a schematic block diagram of the loop antenna 1310 having afirst part 1312 arranged within one of the outer layers 1360 and asecond part 1314 arranged within the inner layer 1340. The loop antenna1310 represents an implantable device having an antenna partiallyembedded within a dielectric medium and partially exposed to thesurrounding tissue of the patient. For example, the loop antenna 1310 ofFIG. 21 may represent the loaded loop antenna 1210 of FIG. 14, which ispartially insulated within a layer 1240 of a dielectric medium, afterimplantation.

FIG. 22 is a schematic block diagram of the loop antenna 1310 arrangedcompletely within the inner layer 1340. The loop antenna 1310 representsan implantable device having an antenna fully embedded within aninsulating layer of dielectric medium. For example, the loop antenna1310 of FIG. 22 may represent the loaded loop antenna 1210 of FIG. 16,which is fully insulated within a layer 1240 of a dielectric medium,after implantation.

The effects of the dielectric medium on the Return Loss Response of anexample antenna arrangement are numerically simulated in FIG. 23 usingcomputer modeling. FIG. 23 is a graph plotting the lowest dip of theReturn Loss Response of the loop antenna 1310 for each arrangement shownin FIGS. 19-22 as a function of frequency. The graph 1500 has a firstaxis 1510 representing Return Loss Response (dB) and a second axis 1520representing frequency. The first axis 1510 ranges from about −30 dB toabout 3 dB and the second axis 1520 ranges from about 0.1 GHz to about0.5 GHz. As noted in the legend 1505, symbols including circles,triangles, and diamonds have been added to the Return Loss Responsecurves of the graph 1500 to distinguish the different curves. Thesesymbols do not correspond with actual data points, but rather serve onlyto differentiate the Return Loss Response curves.

The Return Loss Response 1560 of the loop antenna arranged in free space(FIG. 19) is depicted by the unembellished solid curve. The Return LossResponse 1560 of this arrangement provides a base reading to which theother Return Loss Responses may be compared. The Return Loss Response1530 of the exposed loop antenna 1310 of FIG. 20 is depicted by thediamond-dotted curve. The Return Loss Response 1540 of the partiallyinsulated loop antenna 1310 of FIG. 21 is depicted by the circle-dottedcurve. The Return Loss Response 1550 of the fully insulated loop antenna1310 of FIG. 22 is depicted by the triangle-dotted curve.

As shown in FIG. 23, the lowest resonant frequency of the loop antenna(unembellished curve) arranged in free space (see FIG. 19) is about 0.45GHz with a return loss response 1560 of about −6 dB. The lowest resonantfrequency of the exposed loop antenna (diamonds) (see FIG. 20) is about0.19 GHz with a return loss response 1530 of about −16 dB. The lowestresonant frequency of the partially embedded loop antenna (circles) (seeFIG. 21) is about 0.26 GHz with a return loss response 1540 of about −27dB. The lowest resonant frequency of the fully embedded loop antenna(triangles) (see FIG. 22) is about 0.28 GHz with a return loss response1550 of about −19 dB.

Accordingly, the graph 1500 indicates implanting an exposed loop antenna1310 (FIG. 20) within human tissue lowers the resonant frequency andincreases the radiation capability of the antenna arrangement (ascompared to the antenna 1310 arranged in free space-FIG. 19).

Furthermore, partially embedding the loop antenna 1310 within aninsulating layer of dielectric medium (FIG. 21) may shift the resonantfrequency of the antenna to a higher frequency (compare curves 1530 and1540). Fully embedding the loop antenna 1310 within the insulating layerof dielectric medium (FIG. 22) may further shift the resonant frequencyof the antenna (compare curves 1540 and 1550). Loop Antenna

FIG. 34 is a schematic block diagram of an example implantable device3400 including a loop antenna 3410 wound around a housing 3420. In oneembodiment, the loop antenna 3410 is wound around the housing 3420 onlyabout once. For example, the loop antenna 3410 has a length of at leastλ, wherein λ is the effective wavelength for far-field datacommunications. In another embodiment, the loop antenna 3410 is woundaround the housing 3420 multiple times. For example, in one embodiment,the loop antenna 3410 may be wound around the housing a sufficientnumber of times to have the antenna effective in near-field powertransfer and/or communications. In one embodiment, the implantabledevice 3400 does not include a matching circuit.

In one embodiment, the loop antenna 3410 may be partially or fullyembedded within a dielectric layer. In another embodiment, the loopantenna 3410 may be fully exposed to the environment in which theimplantable device 3400 is arranged.

In another embodiment, the housing 3420 may be partially or fullyembedded in a dielectric material. In another embodiment, the housing3420 may be fully exposed.

In general, the loop antenna 3410 is configured to receive power and todeliver the received power to circuitry within the housing 3420. In oneembodiment, the loop antenna 3410 is configured to resonate whenreceiving and transmitting a low frequency signal (e.g., around 6.73MHz). In such an embodiment, the loop antenna 3410 may deliver currentinduced by the received signal to a rechargeable power source 3424within the housing 3420.

In another embodiment, the loop antenna 3410 is configured to resonatewhen receiving and transmitting a higher frequency signal (e.g., around402-405 MHz). When the loop antenna 3410 resonates at higherfrequencies, the loop antenna appears electrically larger than when theloop antenna 3410 resonates at lower frequencies. Accordingly, the loopantenna 3410 may receive and send far-field signals.

In such an embodiment, the loop antenna 3410 may deliver current inducedby the received signal to a communications circuit (e.g., a MICScommunications circuit) 3426 within the housing 3420. The loop antenna3410 also may receive power from the rechargeable power source 3424 anda data or command signal from the communications circuit 3426 andtransmit the data or command signal using the received power.

In another embodiment, the loop antenna 3410 is configured to resonateat multiple frequencies. In such an embodiment, the housing 3420 of theimplantable device may include one or more switching circuits 3422configured to receive current induced on the loop antenna 3410 when asignal is received. The switching circuit 3422 determines the type ofsignal received (e.g., based on the frequency) and may provide power toan appropriate circuit within the housing 3420 based on the type ofsignal received.

For example, in one embodiment, in the example shown in FIG. 34, theswitching circuit 3422 is electrically coupled to the rechargeable powersource 3424 and the communications circuit 3426 within the housing 3420.The switching circuit 3422 may determine whether to forward a signalreceived at the loop antenna 3410 to the power source 3424 forrecharging or to the communications circuit 3426 for analysis.

In another embodiment, the switching circuit 3422 may be electricallycoupled to multiple communication circuits within the housing 3420. Insuch an embodiment, the switching circuit 3422 may determine theappropriate communication circuit to which to forward the receivedsignal.

In other embodiments, additional circuitry may be provided within thehousing 3420 and coupled to the switching circuit 3422 to provideadditional functionality to the implantable device 3400. The switchingcircuit 3422 may direct power to the appropriate circuitry (e.g., basedon the frequency of the received signal, based on instructions containedwithin the signal, etc.).

In one embodiment, inductive coupling between the loop antenna 3410 andone or more unbalanced antennae (e.g., see FIG. 24) increases the numberof resonant frequencies of the loop antenna 3410. Accordingly, suchinductive coupling may increase the range of applications capable ofbeing performed by the implantable device 3400.

Antennae Array

An implantable device also may include an antenna arrangement includingan array of antennae. For example, FIG. 24 is a schematic block diagramof an example embodiment of an implantable device 1600 including aninner housing 1620 coupled to an antennae arrangement 1650. The innerhousing 1620 may contain an RF module and a treatment module asdisclosed above with reference to FIGS. 1 and 2.

The antenna arrangement 1650 includes a loop antenna 1610 coupled to anarray 1660 of antennae that may include any combination of balanced andunbalanced antennae. In the example shown, the array 1660 includesantennae 1631-1639.

In general, the antennae array 1660 may enhance the flexibility andutility of the implantable device by providing radiation patterndiversity, spatial diversity, and/or polarization diversity. Forexample, each antenna within the antennae array 1660 may be tuned toresonate at a unique resonant frequency, thereby providing radiationpattern diversity. Different types of signals (e.g., power andcommunication) may be radiated over different frequency ranges. Spatialdiversity of the antennae within the antennae array 1660 may enable anexternal component to identify a location of the implantable device.Polarization diversity may enhance coupling flexibility of theimplantable device by reducing or removing dependencies of antennaorientation or antenna performance.

In some embodiments, two or more antennae of the array 1660 may becapacitively coupled to one another to increase the aperture of theantenna arrangement. In one embodiment, at least one of the antennae1631-1639 of the antennae array 1660 is an unbalanced antenna. In otherembodiments, one or more antennae of the array 1660 may be decoupledfrom the loop antenna 1610 to inhibit interference with radiation fromother antennae, other components, and/or other devices.

The implantable device 1600 also may include an optional insulatinglayer 1640. In different embodiments, the insulating layer 1640 maypartially or completely surround the antennae arrangement 1650. In theexample shown in FIG. 24, the loop antenna 1610 and six of theadditional antennae 1631-1636 of the array 1660 are fully embeddedwithin the insulating layer 1640. Antennae 1637 and 1639 of the array1660 are partially embedded within the insulating layer 1640 and antenna1638 is fully exposed to any surrounding medium (e.g., air, tissue,etc.).

Example Applications

The above diagrams and numerical simulations provide the conceptualbasis for understanding the following example embodiments of implantabledevices configured in accordance with the principles of the presentdisclosure as described herein.

FIGS. 25-27 illustrate a first example embodiment of an implantabledevice 2000 including a loop antenna 2010 wrapped around an innerhousing 2020 containing components configured to implement telemetry andtreatment, such as RF module 110, a treatment module 115, and arechargeable battery 117 of FIGS. 1 and 2. The loop antenna 2010 couplesto the circuitry via antenna port 2015 defined in the inner housing2020.

In one embodiment, the loop antenna 2010 may be wrapped once around aperimeter of the inner housing 2020. In another embodiment, the loopantenna 2010 may be wrapped about only a portion of the perimeter. Inother embodiments, however, the loop antenna 2010 may be wound aroundthe perimeter of the inner housing 2020 multiple times. In the exampleshown, the loop antenna 2010 is wrapped around the inner housing 2020about four times (see windings 2012, 2014, 2016, 2018 of FIG. 27).

In one embodiment, the loop antenna 2010 may be wrapped around the innerhousing 2020 in a helical pattern (e.g., see FIGS. 25 and 27). Inanother embodiment, the loop antenna 2010 may be wrapped about the innerhousing 2020 in a spiral pattern. Advantageously, a helical windingpattern allows for a smaller circumference than a spiral windingpattern. A spiral winding pattern, however, allows for a thinner formfactor than a helical winding pattern.

In another embodiment, the loop antenna 2010 may include sections woundin a spiral shape and other sections wound in a helix shape. Forexample, in one embodiment, the spiral shaped sections may facilitaterouting the loop antenna 2010 around lead sockets of the implantabledevice 2000 and the helical-shaped sections may be wound around the restof the implantable device 2000. Accordingly, the antenna configurationfor each implantable device may be selected based on the intendedimplantation site and/or the intended function.

A first unbalanced antenna 2030 may be capacitively coupled to the loopantenna 2010. In the example shown, the first unbalanced antenna 2030includes an inverted-L antenna. In such an embodiment, the firstunbalanced antenna 2030 includes a first section 2032 extendingoutwardly from the inner housing 2020 and wrapping around the loopantenna 2010. The first unbalanced antenna 2030 also includes a secondsection 2034 having a generally planar surface extending substantiallyparallel to the coils of the loop antenna 2010. In other embodiments,the first unbalanced antenna 2030 may include any unbalanced antenna(e.g., a zigzag antenna, a helical antenna, a spiral antenna, a foldedantenna, a serpentine antenna, or any other suitable antenna).

In the example shown, the loop antenna 2010 and the unbalanced antenna2030 are fully enclosed within (i.e., fully insulated by) an outer layer2040 of a dielectric material. In another embodiment, the outer layer2040 may enclose only one of these antennae 2010, 2030. In anotherembodiment, portions of one or both antennae 2010, 2030 may be enclosedwithin (i.e., partially insulated by) the outer layer 2040. In otherembodiments, however, the antennae 2010, 2030 may be exposed (i.e.,neither antenna may be enclosed within the outer layer 2040).

Therapy ports 2060 (FIG. 26) for receiving therapy elements, such astherapy elements 170 of FIGS. 1 and 2, also may be defined in the outerlayer 2040. In general, the therapy ports 2060 are configured to acceptconnectors for therapy elements (e.g., lead connectors) in order to forman electrical connection between the therapy elements and componentscontained in the inner housing 2020 (e.g., the treatment module and arechargeable battery).

In one embodiment, the outer layer 2040 defines suture passages 2048 bywhich the implantable device 2000 may be secured in position within thepatient. In the example shown in FIGS. 25 and 26, the outer layer 2040defines three suture passages 2048 extending through the implantabledevice 2000.

FIGS. 28-30 illustrate a second example embodiment of an implantabledevice 2100 including a loop antenna 2110 wrapped around an innerhousing 2120 containing treatment components, such as RF module 110,treatment module 115, and rechargeable battery 117 of FIGS. 1 and 2. Theloop antenna 2110 couples to the RF module and the treatment module viaantenna port 2115 defined in the inner housing 2120. As in the firstimplantable device 2000, the loop antenna 2110 may be wrapped around aperimeter of the inner housing 2120. In the example shown, the loopantenna 2110 is wrapped around the inner housing 2120 about four times(see windings 2112, 2114, 2116, 2118 of FIG. 29). In other embodiments,however, the loop antenna 2210 may be wrapped fewer or greater times.

A second unbalanced antenna 2130 may be capacitively coupled to the loopantenna 2110. In the example shown, the unbalanced antenna 2130 isanother serpentine antenna that is moderately coupled to the loopantenna 2110. In such an embodiment, the second unbalanced antenna 2130includes a first section 2132 having a planar surface extendingsubstantially parallel and in proximity to the loop antenna 2110 and asecond section 2134 having a planar surface extending substantiallyparallel to, but spaced from the loop antenna 2110.

In the example shown, the loop antenna 2110 and the second unbalancedantenna 2130 are enclosed within (i.e., fully insulated by) an outerlayer 2140 of a dielectric material. In another embodiment, the outerlayer 2140 may enclose only one of these antennae 2110, 2130. In anotherembodiment, portions of one or both antennae 2110, 2130 may be enclosedwithin (i.e., partially insulated by) the outer layer 2140. In otherembodiments, however, the antennae 2110, 2130 may be exposed (i.e.,neither antenna may be enclosed within the outer layer 2140).

Therapy ports 2160 for receiving therapy elements, such as therapyelements 170 of FIGS. 1 and 2, also may be defined in the outer layer2140. In general, the therapy ports 2160 are configured to acceptconnectors for therapy elements (e.g., lead connectors) in order to forman electrical connection between the therapy elements and the components(e.g., the treatment module and a battery) contained in the innerhousing 2120. In an embodiment, the outer layer 2140 also defines suturepassages 2148 by which the implantable device 2100 may be secured inposition within the patient.

FIGS. 31-33 illustrate a third example embodiment of an implantabledevice 2200 including a loop antenna 2210 wrapped around an innerhousing 2220 containing an RF module and treatment module, such as RFmodule 110 and treatment module 115 of FIGS. 1 and 2. The loop antenna2210 couples to the RF module and the treatment module via antenna port2215 defined in the inner housing 2220. As in the first implantabledevice 2000, the loop antenna 2210 may be wrapped around a perimeter ofthe inner housing 2220. In the example shown, the loop antenna 2210 iswrapped around the inner housing 2220 about four times (see windings2212, 2214, 2216, 2218 of FIG. 29). In other embodiments, however, theloop antenna 2210 may be wrapped fewer or greater times.

A third unbalanced antenna 2230 may be decoupled from the loop antenna2210. In the example shown, the unbalanced antenna 2230 is a zigzagantenna that is decoupled from the loop antenna 2210. In such anembodiment, the surface 2236 of the third unbalanced antenna 2230 mayextend substantially perpendicular to the coils of the loop antenna2210.

In the example shown, the loop antenna 2210 and the second unbalancedantenna 2230 are enclosed within (i.e., fully insulated by) an outerlayer 2240 of a dielectric material. In another embodiment, the outerlayer 2240 may enclose only one of these antennae 2210, 2230. In anotherembodiment, portions of one or both antennae 2210, 2230 may be enclosedwithin (i.e., partially insulated by) the outer layer 2240. In otherembodiments, however, the antennae 2210, 2230 may be exposed (i.e.,neither antenna may be enclosed within the outer layer 2240).

Therapy ports 2260 for receiving therapy elements, such as therapyelements 170 of FIGS. 1 and 2, also may be defined in the outer layer2240. In general, the therapy ports 2260 are configured to acceptconnectors for therapy elements (e.g., lead connectors) in order to forman electrical connection between the therapy elements and the components(e.g., the treatment module and a battery) contained in the innerhousing 2220. In an embodiment, the outer layer 2240 also defines suturepassages 2248 by which the implantable device 2200 may be secured inposition within the patient.

The above specification, examples, and data provide a completedescription of the manufacture and use of the composition of theinvention. Since many embodiments of the invention can be made withoutdeparting from the spirit and scope of the invention, the inventionresides in the claims hereinafter appended.

1. An implantable medical device comprising: an inner housing containinga processor and a communications circuit; an antenna arrangementincluding a first antenna and a second antenna capacitively coupled tothe first antenna, the first antenna being wrapped circumferentiallyaround the inner housing, the first antenna having a first port at whichthe first antenna enters the inner housing, and the first antennaincluding a loop antenna, the second antenna being arranged external ofthe inner housing, the second antenna having a second port at which thesecond antenna enters the inner housing, the second antenna beingelectrically coupled to the communications circuit via the second port;wherein the implantable medical device is configured for implantationwithin a body of a patient.
 2. The implantable medical device of claim1, wherein the loop antenna is electrically coupled to thecommunications circuit via the first port.
 3. The implantable medicaldevice of claim 1, wherein the inner housing includes a rechargeablepower source to which the loop antenna is electrically coupled via thefirst port.
 4. The implantable medical device of claim 3, wherein theinner housing also contains a switching circuit, wherein the loopantenna is electrically coupled to the switching circuit, and whereinthe switching circuit selectively directs power obtained at the loopantenna to the rechargeable power source and selectively directs data orcommand signals obtained at the loop antenna to the communicationscircuit.
 5. The implantable medical device of claim 1, wherein thesecond antenna of the antenna arrangement is configured to receive aresonant signal at the second port, the resonant signal having afrequency of about 401-406 MHz.
 6. The implantable medical device ofclaim 1, further comprising a dielectric outer layer disposed about atleast a portion of the inner housing.
 7. The implantable medical deviceof claim 1, further comprising a dielectric outer layer disposed aboutat least a portion of the first antenna.
 8. The implantable medicaldevice of claim 1, further comprising a dielectric outer layer disposedabout at least a portion of the second antenna.
 9. The implantablemedical device of claim 1, wherein the loop antenna is wound about theinner housing at least once.
 10. The implantable medical device of claim9, wherein the loop antenna is wound about the inner housing asufficient number of times for near-field operations.
 11. Theimplantable medical device of claim 1, wherein the second antennaincludes an unbalanced antenna.
 12. The implantable medical device ofclaim 11, wherein the second antenna includes an array of unbalancedantennae.
 13. The implantable medical device of claim 12, wherein theunbalanced antennae of the array are coupled together in series.
 14. Theimplantable medical device of claim 12, wherein at least two of theunbalanced antennae in the array are capacitively coupled to the loopantenna.
 15. The implantable medical device of claim 12, wherein theadditional antennae are positioned and oriented about the inner housingto reduce polarization loss of the implantable medical device.
 16. Theimplantable medical device of claim 12, wherein the additional antennaeare configured to enable location of the implantable medical devicerelative to an external signal source.
 17. The implantable medicaldevice of claim 1, wherein the loop antenna is a helical loop antenna.18. A method for communicating with an implantable device, the methodcomprising: providing an implantable device including a loop antennawound around an exterior of an inner housing containing a processor, acommunications circuit, a rechargeable power source, and a switchingcircuit, the implantable device also including a second antennacapactively coupled to the loop antenna; implanting the implantabledevice within the patient; transmitting a power signal to theimplantable device to provide power to the rechargeable power source,the power signal having a first frequency; and transmitting acommunications signal to the implantable device to provide data orcommands to the communications circuit, the communications signal havinga second frequency that is higher than the first frequency.
 19. Themethod of claim 18, wherein transmitting the communications signal tothe implantable device comprises transmitting the communication signalhaving the second frequency of about 402-405 MHz.